If they do go AMD all round, launching the next generation of Xbox a year or two early would likely leave them behind a whole RDNA/ZEN generation & node process. Plus, Sony are the market leaders and the gen will probably start when they say it does (likely 2028).
If Sony have a $499-599 Pro and MS have a ~$499 refresh XSX with the same performance as the launch model; PS will be a far better value proposition with vastly superior performance for 2-3yrs. Then if MS release in 2026/2027 they'd have a power lead on a console that barely anyone is inclined to rush their games to. Then when Sony releases a PS6 in 2028 they'd have the power lead again. Power isn't everything of course, but I'd argue such an approach would either be really poor tactics or a sign of an intentional, slow "stealth" exit from the console business, showing their clear intention for PC, Cloud & other devices not as additions but in place of console.
The only 2027 Xbox that makes sense if Sony are dropping PS6 in 2028, would be a crazy curveball like an ARM/NvidiaRTX APU or even an Intelx86/IntelARC APU.
...
I think the best generation approach is 8yrs with a standard launch console and a pro/slim at the halfway mark. If their is a lite console at launch it needs to be 1/2 GPU, 3/4 RAM+Bandwidth & 1/2 Storage with all other specs and featuresets identical (XSS falls way short). 5-6yr spans at this point would mean relatively small leaps in hardware technology, games not really getting to take advantage of the platform, pair this with some degree of diminishing returns and the industry taking much more iterative approaches to various properties already; and these four things will all compound each other resulting in less impressive experiences.